A theoretical substantiation of calculation of the thermodynamic cycle of engines with detonation fuel combustion, which is realized in propulsion modules of pulse detonation engines, has been given. A system of equations for calculation of the parameters of detonation combustion waves under different conditions of their excitation has been obtained. On their basis, investigations of the influence of different factors on the parameters of detonation combustion waves and accordingly on the cycle work, thermal efficiency, and specific parameters of pulse detonation engines have been performed. It has been established that the loss due to the irreversibility of the process of heat supply in detonation combustion waves is much lower when propulsion modules are installed in the heated-gas flow. It has been shown that the temperature of the working medium fed to propulsion modules is the determining factor influencing the thermodynamic efficiency of the detonation-fuel-combustion cycle. Generalized characteristics in the form of one-parameter dependences of the specific parameters of propulsion modules of pulse detonation engines on the temperature of the working medium fed to them have been obtained.